[Premium-Rx] Filter phase response

[George Georgevits]

Interesting article John. I note that he is not testing and comparing just
filters, but receivers containing the filters.

I can assure you that if you do the maths, filter theory will tell you that
for narrow band filters, linear phase response filters (ie. those exhibiting
a Bessel response) are the least prone to ringing.

Having said this, with a communications receiver, there are a host of other
confounding factors such as AGC response, overall gain etc. etc.

Regards,
George Georgevits
Power and Digital Instruments Pty Ltd


-----Original Message-----
From: premium-rx-bounces at ml.skirrow.org
[mailto:premium-rx-bounces at ml.skirrow.org]On Behalf Of John Reed
Sent: Wednesday, 8 October 2003 9:32 AM
To: Premium RX
Subject: Re: [Premium-Rx] Filter phase response



----- Original Message -----
From: "George Georgevits" <georgg at bigpond.net.au>
To: "Premium-RX LIST" <premium-rx at ml.skirrow.org>
Sent: Tuesday, October 07, 2003 4:33 PM
Subject: RE: [Premium-Rx] Marconi LP Filter


> Interesting that no-one has mentioned the IF filter group delay or PHASE
> RESPONSE!
>
> I think you will find this is responsible for many of the effects
described
> qualitatively by others here. For example, the amount of ringing exhibited
> by a filter is a function of its phase response. When a receiver is used
for
> data reception, linear phase response (ie. flat group delay) is what it is
> all about.

Check out this web page from the Lowdown:

http://www.lwca.org/library/articles/jtreed/impr/impr1.htm

This article compares a digital, linear phase 100 Hz filter in a W-J HF-1000
with a 100 Hz crystal filter from an old surplus receiver.  Take a look at
these two impulse responses and see if you think linear phase is the answer
to ringing problems.

John Reed






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